This article analyses the origin and the main features of the right to be heard as a general principle of European Union (EU) law. It also analyses the EU customs rules regarding this principle, which are included in the regulation 952/2013 establishing the Union Customs Code and in the Commission Implementing Regulation (EU) 2015/2447. To this end, the analysis, also based on European Court of Justice (ECJ) case law, refers to possible restrictions to the right to be heard and the consequences arising from its violation. It highlights how the right to be heard protects not only the interests of individual customs operators, but also the interest of the EU in the proper conduct of relations between EU Member State authorities.